1. Field of the Invention
The present invention relates to a magnetoresistive head and, more particularly, a magnetoresistive head capable of reading signal information by converting a change in magnetic field generated from a magnetic recording medium into a change in electric resistivity by use of spin valve magnetoresistance effect, upon reading information signal from the magnetic recording medium.
2. Description of the Prior Art
As a device for reading information signals from the magnetic recording medium such as a hard disk, a magnetic card, a magnetic tape, the magnetoresistive head employing the spin valve magnetoresistance effect has been proposed in Patent Application Publication (KOKAI) U.S. Pat. No. 5,206,590.
The magnetoresistive head has a structure shown in FIGS. 1A and 1B, for example.
In FIGS. 1A and 1B, a lower ferromagnetic layer 2, a nonmagnetic metal layer 3, an upper ferromagnetic layer 4, and an antiferromagnetic layer 5 are formed in that order on a substrate 1 having large electric resistance. Respective layers from the lower ferromagnetic layer 2 to the antiferromagnetic layer 5 have a plane rectangular shape. In addition, a pair of lead electrodes 6a, 6b are formed in the longitudinal direction at a distance on the antiferromagnetic layer 5, thus completing a magnetoresistive head. As materials constituting these layers, an iron-manganese (NiFe) is used as upper and lower ferromagnetic layers 2, 4, a copper (Cu) is used as the antimagnetic metal layer 3, and an iron-manganese (FeMn) is used as the antiferromagnetic layer 5, for example. In FIGS. 1A and 1B, a Z-axis denotes the direction of film thickness.
The upper ferromagnetic layer 4 is magnetized by exchange coupling of the antiferromagnetic layer 5, and the direction of magnetization is a width direction (an X axis direction in FIG. 1B). The lower ferromagnetic layer 2 is magnetized in the longitudinal direction (a Y axis direction in FIG. 1B). It is preferable that the direction of magnetization of the lower ferromagnetic layer 2 intersects orthogonally the direction of magnetization of the upper ferromagnetic layer 4 if the external signal magnetic field is zero. The external signal magnetic field is a magnetic field generated from the magnetic recording medium, and is generated in the width direction of each layer (an X axis direction). The direction of magnetization of the upper ferromagnetic layer 4 is perpendicular to the surface of the magnetic recording medium whereas the direction of magnetization of the lower ferromagnetic layer 2 is formed along the surface of the magnetic recording medium.
If the external signal magnetic field is applied to such spin valve magnetoresistive head, the direction of magnetization of the lower ferromagnetic layer 2 is inclined at an angle corresponding to the strength and direction of the external signal magnetic field.
A component of the direction of magnetization of the lower ferromagnetic layer 2 in the direction opposite to the direction of magnetization of the upper ferromagnetic layer 4 causes scattering of electrons passing through these layers, thus increasing electric resistance of entire layers. On the other hand, a component of the direction of magnetization of the lower ferromagnetic layer 2 in the same direction as the direction of magnetization of the upper ferromagnetic layer 4 decreases scattering of electrons passing through these layers, thus decreasing electric resistance of entire layers.
The electric resistance of the sense current area S is changed in proportion to cosine of angle difference .theta. between the direction of magnetization of the lower ferromagnetic layer 2 and the direction of magnetization of the upper ferromagnetic layer 4, i.e., cos.theta..
In addition, in order to change the electric resistance to the signal magnetic field generated from the magnetic recording medium linearly, the direction of magnetization of the lower ferromagnetic layer 2 is intersected with the direction of magnetization of the upper ferromagnetic layer 4 under the condition that the external signal magnetic field is zero. This signal magnetic field is applied to the same direction as or the opposite direction to the direction of magnetization of the upper ferromagnetic layer 4, i.e., the fixed direction of magnetization.
Thereby, as shown in FIG. 1C, a relation between the external signal magnetic field H and the electric resistance .DELTA.R[R(H)-Ro(H=0)] can be derived.
In case the signal magnetic field generated by the magnetic recording medium is converted into an electric signal, a change in the electric resistance due to the signal magnetic field can be converted into a change in electric voltage by passing a constant current between a pair of lead electrodes 6a, 6b. The change of the voltage is used as a reproducing electric signal. This is the same in the embodiments described hereinafter.
In addition, a width of a sense area S which reads a signal magnetic field by a spin valve magnetoresistance effect has been defined by a distance between the pair of lead electrodes 6a, 6b.
However, according to the laminated layer structure shown in FIG. 1A, a leakage magnetic field from a side portion of the upper ferromagnetic layer 4 enters into a side portion of the lower ferromagnetic layer 2 and acts as a bias magnetic field even when the external signal magnetic field is in a zero state.
Therefore, the direction of magnetization of the lower ferromagnetic layer 2 made of a soft magnetic material is inclined by the leakage magnetic field, so that the direction of magnetization of the lower ferromagnetic layer 2 does not intersect orthogonally with the magnetization of the upper ferromagnetic layer 4. As a result, there is caused a drawback that the electric resistance (specific resistance) cannot change linearly with respect to the signal magnetic field and thus the voltage waveform as a reproducing signal is distorted.
On the contrary, a magnetoresistive head wherein the direction of magnetization of the upper magnetic layer is not fixed and varied by the external signal magnetic field along with the direction of magnetization of the lower magnetic layer has been set forth in Patent Application Publication (KOKAI) 2-61572. But, although influence of the leakage magnetic field from the ferromagnetic layer need not be considered, there is no recitation in this Publication how to adjust a relative angle between directions of magnetization of two ferromagnetic layers concretely. In practice, it is hard to operate the magnetoresistive head linearly by intersecting directions of magnetization of these layers with each other.
As shown in FIG.2, a signal magnetic field H.sub.t of a track adjacent to the magnetic recording medium beneath the lead electrode 6a leaks into the sense area S via soft magnetic layers 2, 4 formed immediately below the lead electrodes 6a, 6b. Therefore, there has been caused another drawback that noise enters into a reproducing electric signal.
In addition, the sense area S must be defined essentially by the distance between two lead electrodes 6a, 6b. However, the spin valve magnetoresistance effect is in practice caused in a wider area than that defined by the distance between two lead electrodes 6a, 6b. Thus, there has been caused another drawback that the sense area for reading the signal magnetic field becomes vague, so that it is difficult to clearly define the sense area.